The present invention relates to a method of distance measurement between wireless communication devices in a wireless communication system, and more particularly, to a method combining distance measurement derived from received signal strength indication (RSSI) and measurement of round trip time (RTT) to estimate a distance between wireless communication devices in a wireless communication system.
In IEEE 802.11 standard, TOD (Time of Departure) and TOA (Time of Arrival) both are timing parameters utilized for signal transmission to represent a period at which a packet is transmitted from a transmitting antenna and a period at which a packet is received by a receiving antenna, respectively. Accordingly, via recording the TOD and TOA corresponding to a delivered signal, a transmission period (e.g. a round trip time) can be adaptively obtained to derive a transmission distance between two stations or wireless communication devices.
However, before a timing measurement handshake is processed between the two wireless communication devices, each wireless communication device is necessary to apply a calibration flow to compensate a digital latency or an analogy circuit delay, so as to obtain an accurate distance between two wireless communication devices. Specifically, the available calibration flow may utilize a pre-stored look-up table in each wireless communication device. Nevertheless, the look-up table may consume a lot of memory space due to different vendor requirements or sensitivity temperature of circuits. Alternatively, applying calibration loops to the receiver/transmitter is practicable, but more hardware costs may be anticipated and a serious synchronization issue for the receiver/transmitter is inevitable.
Therefore, it has become an important issue to provide another efficient method for distance measurement between two wireless communication devices to avoid the utilization of a look-up table or calibration loops for the wireless communication system.